Essential to an understanding of the mechanisms whereby drugs, hormones and ions exert their effects on contractility of smooth muscles is an understanding of the fundamental mechanochemical and mechanical aspects of the contractile process. We will study the way in which the ovarian hormones affect contractility of the myometrium by examining their mechanical behavior and chemical composition under the influence of these hormones (estrogen, progesterone, and pregnancy). The role of calcium and calcium distribution under these conditions will be reevaluated in terms of contractility. Length-tension and force- velocity and series elasticity properties will be examined in order to define the behavior of the myometrium under the cyclic influence of hormones. The behavior of the myometrium will be compared with other smooth muscles whose composition and contractility are not altered by these hormones. The action of various drugs and ions which are known to potentiate or depress contraction will be studied and used as probes to alter specific processes underlying contraction.